When two bodies, particularly of unlike materials, are brought together into intimate contact, there is likely to be a redistribution of electrons across the interface and an attractive force is established as equilibrium is achieved. When the bodies are separated, work must be done in opposition to these attractive forces. The expended energy reappears as an increase in electrical tension or voltage between the two surfaces and the surfaces are said to be electrically charged with respect to each other. If a conductive path is available, the charges thus separated will reunite (e.g. equilibrate) immediately. If no such path is available, as would be the case with insulators or non-conductors, the potential increase with separation may easily reach values of several thousand volts. A charge may be either positive (+) or negative (-) denoting a deficiency or excess of electrons, respectively. A surface that has an excess or deficiency of one electron in every one hundred thousand atoms is strongly charged.
Like charges repel each other and unlike charges attract because of forces resident in the electrical fields that surround them. Accordingly, as a result of the repulsive forces associated with like charges, it is apparent that the charge on a charged object will be located on the exterior surface thereof. These forces have a strong influence on nearby objects. If the neighboring object is a conductor it will experience a separation of charges by induction. Its repelled charge is free to give or receive electrons as the case may be; if another conductor is brought near, the transfer may occur through the agency of a spark, very often an energetic spark. Such charge transfer actions are known to adversely affect or even electronically destroy a number of electronic devices which are sensitive to electricity and, for example, static electricity. Microcircuit devices such as integrated circuit chips, for example, may be damaged by electrostatic discharge prior to their incorporation into electrical or electronic equipment.
In order to prevent electrostatic breakdowns, containers, in which such devices are stored and even transported, have been provided with means for short-circuiting the device terminals or pins during storage. This short-circuiting serves to prevent the accumulation of potentially damaging static charges on the device. The container represented in U.S. Pat. No. 4,171,049 accomplishes this task by utilizing a series of conductive slots or grooves into which a number of static electricity sensitive devices maybe serially inserted and later serially dispensed to manufacturing equipment. Other containers have been developed for portable use as in the device replacement market. These containers have taken the form of small, box-like containers that may house conductive sponge or foam sheets into which the device terminals may be temporarily embedded. Exemplary of such a container is the container disclosed in U.S. Pat. No. 4,333,565.
Containers which are to be utilized for storage and transportation of repair or replacement electrically sensitive devices to an on-site field location should possess several characteristics and/or capabilities some of which are quite different from those which are normally associated with containers utilized for storing and sorting devices for incorporation into originally manufactured equipment. For example, besides possessing the ability to inhibit electrostatic charge buildup and shielding the contents from electrical fields the portable containers or work stations should also provide protection from mechanical shock and vibration. Furthermore, the portable containers should be of light weight construction and easy to use when gaining access to the equipment which is to be repaired. Another desirable feature of such a portable container is its capability of storing static sensitive devices of different sizes and shapes without an attendant change in size or shape in the container itself. Reusability and tamper security are still other desirable qualities. Of course, cost economy is also very important.
Unfortunately, the prior portable containers which have heretofore been utilized in storage and transportation of static electricity sensitive devices for field use have been lacking in a number of the above described perferred physical characteristics and capabilities. This situation may be attributable to the fact that many of these containers were specifically designed for on-line in-factory use in the original manufacture of electronic or electrical equipment systems. Thus, these containers did not have to meet many of the requirements which were necessary or, at least, highly desirable in a portable container. Exemplary of the shortcomings of the on-line containers was the fact that, in general, the containers were designed so that each type of container would contain only one particular electrically sensitive device. Accordingly, the type of electrically sensitive device contained within the container would be known by merely viewing the physical configuration or other indicia located on the exterior of the container. This system of identification was believed necessary since unnecessary opening of the container to view the electrically sensitive devices was undesirable since the act of opening the container destroyed the shielding effect of the container. This situation also led to difficulties since a great number of different container designs or sizes became necessary to identify all of the various different types of electrically sensitive devices. While such a situation, although not preferable, may have been tolerable in the on-line in-plant manufacturing situation where ample storage facilities were readily available, such an identification system was clearly unsatisfactory for field repair situations since the repair technician could not physically carry such a vast array of cases with him for on-site repair. Accordingly, the repair technician generally had to carry several different devices within a single container and, in many cases, had to carry several containers each containing differing electrically sensitive devices. This development resulted in an identification problem since the case which shielded the electrically sensitive device from the possible harmful effects of external electrical forces had to be opened by the field technician in order to ascertain the location of a given electrically sensitive device. In many instances such action unnecessarily subjected the electrically sensitive devices to potentially hazardous electrical fields or charges and rendered the devices electrically defective. This situation was undesirable in that the devices were unnecessarily destroyed and the repair time was extended in that new repair parts would have to be obtained.
Accordingly, the need for a container which effectively shielded electrically sensitive devices from the adverse effects of external electrical forces and static charges wherein the container was provided with a window for viewing and identifying the contents without opening of the container arose. Of course the window portion of the container, as is the case with the remaining enclosure portion of the container, had to be electrically conductive and in electrical conductive communication with the remainder of the container for the shielding effect of the container to be complete. Normal glass could not be utilized as a window material since glass is a non-conductive material and static electric charges could build up thereon. Furthermore, external electrical fields could penetrate the interior of the container by way of the glass window. The presence of an electrical charge on the window portion of the container and/or electrical penetration of the interior of the container could well adversely effect the electrically sensitive devices contained therein.